The present invention relates to an electric rotating machine and a hybrid car provided with the same.
There has been a demand for an electric rotating machine, more specifically, a permanent-magnet-type electric rotating machine for driving a vehicle, including an inverter for controlling the same having a reduced size and capable of providing an increased output power. There has been a demand particularly for a permanent-magnet-type electric rotating machine capable of producing high torque at low operating speeds and of providing high output power at high rotating speeds. Therefore, the conventional permanent-magnet-type electric rotating machine is an embedded permanent-magnet-type electric rotating machine with salient poles using low field magnets for high-speed rotation and capable of using reluctance torque. See, for example, JP-A 1998-126985.
A rotor core on the side of a permanent-magnet stator and a rotor core on the side of the center axis of a permanent-magnet rotor are connected by a bridge for enhancing the mechanical strength withstanding the centrifugal force. See, for example, JP-A 2006-187189.
A permanent-magnet-type electric rotating machine for driving a vehicle is required to produce a very high torque for conformation. Usually, the output torque of an electric rotating machine can be increased by increasing the current supplied to the stator coils. However, an increased current increases heat generated by the electric rotating machine and, therefore, a thermal requirement places a limit on current density. Thus, the magnetic flux of the permanent magnets of the permanent-magnet-type electric rotating machine needs to be effectively used to make the permanent-magnet-type electric rotating machine produce the highest possible torque.
The effective magnetic flux of the permanent magnets of the embedded permanent-magnet-type electric rotating machine can be increased by embedding the permanent magnets at a small depth to reduce leakage flux. The embedded permanent-magnet-type electric rotating machine for driving a vehicle is operated at high rotating speeds. Therefore, the permanent magnets of the embedded-magnet type electric rotating machine needs to have mechanical strength sufficient for securely holding the embedded permanent magnets in place against centrifugal force that acts on the permanent magnets and capable of withstanding operations at high rotating speeds.
When the bridge is used for enhancing the mechanical strength withstanding the centrifugal force, it is possible that the effective magnetic flux of the permanent magnets is less than that of a electric rotating machine not provided with any bridge because the bridge is a magnetic member similar to the core.